Alternating current translating system



Nov. 11, 1941. K. FREUDENHAMMER ALTERNATING CURRENT TRANSLATING SYSTEM Filed June 29, 1939 2 Sheets-Sheet l FURNACE THERMO COUPLE IRRANGED AT 63 FUR/V1455 5 THERMO COUPLE Nov. 11, 1941. K. FREUDENHAMMER 2,252,175

ALTERNATING CURRENT TRANSLATING SYSTEM Filed June 29, 1959 2' sheets-sheet 2 k E W TOR HIGH- FREQUENCY f GEN TIME RELAY RECT/ Patented Nov. 11, 1941 ALTERNATING CURRENT TRANSLATING SYSTEM Klaus Freudenhammer, Berlin-Charlottenburg,

Germany,

assignor to Patentverwertungs- Gesellschaft mit beschrankter Haftung Hermes, Berlin, Germany, a corporation of Germany Application June 29, 1939, Serial No. 281,859

' In Germany July 5, 1938 28 Claims.

This invention relates to alternating current systems for energizing high-frequency induction furnaces.

To supply high-frequency induction furnaces with energy, high-frequency machines driven by asynchronous motors are generally employed. This system has the disadvantage that the highfrequency machine develops its full power only at a given frequency. The system contains a capacitor which is series or parallel-connected with the furnace coil, and the oscillation circuit thus obtained is tuned to the frequency of the machine. If the inductance of the furnace coil varies as a result of the melting or annealing process, a corresponding capacity compensation is necessary to maintain resonance. This compensation is brought about with the aid of a complicated switching device which permits a coarse regulation only. Individual condensers or condenser groups are switched in or out when the fusing or annealing process is temporarily interrupted.

It has further been proposed to supply highfrequency inductance furnaces with energy through controllable gas or vapor discharge devices. Such a supply system, in principle, is capable of permitting a frequency-responsive power control if the input or output circuit of the system of discharge devices is provided with control apparatus such as a stepped input transformer. The known proposals, however, are of little practical value as the regulating devices required by them for bringing about a proper regulation are intricate and consume too much energy.

An object of the invention is to provide a system for supplying high-frequency induction furnaces with energy by means of controllable gas or vapor discharge devices, in which system the above-mentioned drawbacks are removed in a very simple manner. Another object of the invention is to permit any desired, continuous rec,- ulation, within the two limits of the frequency regulation, with a constant power output, or a power control with a constant frequency. A further object is to provide a translating system for energizing high-frequency induction furnaces, which affords a control or regulation of the energizing current, as to frequency, voltage or power, practically without losses.

According to the invention, a translating system for energizing high-frequency induction furnaces from a low-frequency supply source through a frequency-changing translating device is designed so that ignition impulses of the desupply source.

sired high frequency of the furnace current are caused to act on the control electrodes of gas or vapor discharge devices which form part of the afore-mentioned translating device, and these high-frequency ignition impulses are controlled in dependence upon a control voltage having the same frequency as the low frequency It is particularly advantageous to insert in, or to connect with, the control or grid circuit of the translating discharge device a controlling A. C. voltage source having the desired high frequency of the furnace current and whose amplitude is variable at the low frequency of supply voltage fed to the discharge device. This is preferably brought about by inserting a resistance in the circuit of the controlling high-frequency voltage source and by bridging the resistance with the aid of a phaseadjustable control device which is operated at the low frequency of the feed voltage supplied to the discharge device.

According to a further feature of the invention, a two-way rectifier is employed as such a control device, and is provided with controllable auxiliary discharge devices, preferably gas or vapor filled discharge devices, and connected with its output side to the end points of the above-mentioned resistance. The connection between the rectifier and the resistance is effected through a transformer arrangement, and the phase position of the current passing therethrough is variable and controlled at the frequency of the low-frequency supply current, as will be explained hereinafter.

By the use of such a control device, the initiation of the ignition of the main discharge devices is ensured at the exact moment, thus bringing about a very accurate control of the voltage supplied to the furnace. When connecting, in the above-mentioned manner, the twoway rectifiers to the resistances in the circuit of the controlling high-frequency voltage source, the auxiliary discharge devices can be combined in a single auxiliary discharge vessel, a number of two-way rectifiers being provided corresponding to the number of phases of the low-frequency supply voltage.

The foregoing and other objects and features of the invention will be apparent from the following description of the embodiments diagrammatically illustrated in the drawings in which Figs. 1, 2 and 3 show three different translating systems according to the invention, each of these systems serving to controllably operate a highfrequency induction furnace from a low-frequency supply source. Fig. 1 represents a complete translating system, while each of Figs. 2 and 3 shows only a portion of such a system as will be explained hereinafter.

In Fig. 1, the high-frequency induction furnace is designated by 5' and its high-frequency winding by 5. The voltage source, from which the furnace is to be supplied with energy, is designated by I and consists of a three-phase. 50 cycle alternating-voltage network. This supply network is connected through a transformer 2 to the main discharge devices arranged in a discharge vessel 3. To each of the three secondary transformer windings 2' are allotted two anodes 3' connected to each other through a condenser I. In each of the six anode leads of the main discharge vessel 3 is arranged a secondary winding 4' of a transformer 4, whose primary winding is connected to the furnace winding 5. The secondary neutral point of the transformer 2 is connected to the cathode 6' of the main discharge vessel through the reactance coil 6. 8 denotes the grid series resistors and 9 the grid biasing voltage source of the main discharge vessel. The grids 8' allotted to each pair of anodes are connected to the secondary wind ing I of atransformer III, which secondary has its midpoint connected to the grid voltage source 9. The primary windings of each of these transformers III are connected through a resistor II with a controlling voltage source I2 which has the frequency of the furnace current. The voltage source I2 may consist of a tube oscillator whose frequency 'is capable of being varied. The ends of each resistor II are connected to the secondary II' of a transformer I4 whose primary It is connected with the two anodes I3 of a two-way rectifier I3. The auxiliary discharge devices of all the two-way rectiflers I3 are arranged in the same manner as the main discharge devices within a common mercury-vapor filled vessel I5. The primaries II' of transformers I4 have central taps which are connected to the cathode I6 of the auxiliary vessel I5. The two grids I of each rectifier I3 have a common conductor leading to the biasing voltage source I6. In this conductor is inserted the secondary II of a transformer II, the primary I8 of which is energized by a phaseadjustable auxiliary voltage source of low frequency. This auxiliary voltage source consists of a phase shifter I8 connected with the supply network I. The particular construction of the phase shifter I8, shown in Fig. 1, will be described in a later paragraph. I9 denotes the grid series resistors.

The operation of the system described so far is as follows:

During the operation and energization of the induction furnace 5, the system is supplied with alternating current of relatively low frequency (50 cycles) from supply network I. This current ispassed through the main discharge device 3 and its anode circuit containing the reactance coil 6, while being subjected to the translating and modifying control effected by means of the main discharge device 3. This control consists in a conversion of the low frequency current into a current of the higher frequency needed for the operation of the furnace. This high frequency is controlled by the high frequency of the voltage source I2 and also dependent on the modifying bias of a superposed low-frequency control effected by the phaseadjustable voltage source I8 (phase shifter).

The functioning of this frequency-changing control will now be described more in detail.

If one of the control phase voltages supplied to the rectifiers I3 through the transformers II attains the ignition value, that anode of the corresponding rectifier is ignited which is first impressed through the transformer I4 with a positive voltage half-wave of the frequency of the furnace current. In this manner the corresponding resistor I I is short-circuited and then the energization of the transformer I0 connected to the transformer I4 attains a value which increases the control voltage amplitude of the inverter arranged in the main discharge vessel 3 to the ignition value. That main discharge anode 3' is ignited whose grid 8 is first impressed with the positive half-wave of the increased control voltage. If the biasing voltage of the transformer I4 under consideration reverses its direction, the current changes its path of flow from the anode I3, which has been operated up to the present moment, to the other anode connected to the same transformer winding, and the short-circuit of the resistor II is maintained. At the same time the grid 8" of the main discharge gap which 'has been ignited up to this moment, is impressed with a control voltage having an increased negative amplitude, whereas the other main discharge gap belonging to the same pair of anodes 3 is impressed with a control voltage having an increased positive amplitude, whereby the last-mentioned main discharge gap is ignited. The main discharge gap which has been ignited up to this moment is extinguished by the corresponding condenser I. Hereafter the winding of the transformer 4 connected with winding 5' of the furnace is impressed with a complete voltage wave having the frequency of the auxiliary high-frequency voltage source I2. This process is continued with respect to the just-considered pairs of anodes both within the rectifier I3 in vessel I5 and the inverting discharge group in vessel 3, until one of the other control phase voltages, supplied to the vessel I5 through II, is increased to the ignition value. The current then fiows to the corresponding other pair of anodes I3 of the rectifier I3 and to the corresponding other pair of anodes 3' of the inverter vessel 3. By adjusting the phase shifter I8, it is possible to uniformly accelerate or retard the first initiation of ignition of each pair of anodes arranged in the vessel 3 and to thereby effect a continuous control of the voltage supplied or power transmitted to the furnace winding. Independently thereof, it is also possible to continuously control the frequency of the furnace current by varying the frequency of the voltage source I2. The continuous flow of current from one pair of anodes to another pair is ensured by the stabilizing action of the reactor 6.

In the embodiment shown in Fig. 1, the resistors 8 and II are preferably of the variable type. By a suitable selection of the ratio of these resistances, the ratio of the amplitudes of the main control voltage, effective during the conducting and non-conducting periods of the main discharge device, may be adjusted to any desired value. While the above-described embodiment represents a three-phase connection, the systems according to the invention may operate with any desired number of phases. If the number of phases n is greater than two, the number of the pairs of anodes 3' and I3 of the inverters and rectifiers respectively, as well as the number of the corresponding control elements, is equal to n. In a single-phase system, two pairs of anodes 3' and I3, respectively, are employed in the inverter and'rectifler.

The relation between the action of the two control voltages supplied by the voltage sources I2 and I8 may be differently chosen. For instance, the voltage source 2 may supply the grids 8' of the main discharge vessel 3 with an alternating current of constant amplitude and the. desired frequency of the furnace current, and a phase-displaceable voltage of rectangular wave shape. In this case the two voltages of sources l2 and 8 are so rated that only the addition of the rectangular voltage causes the high-frequency impulses to bring about an ignition. Another way is to supply (from source l2) high-frequency direct-current impulses of constant amplitude and sufficient for ignition and to block and release these impulses by means of a phase-adjustable control current (from source l8) having the same frequency as the source I.

The phase-adjustable low-frequency source, represented in Fig. 1 by the phase-shifter I8, may be controlled at will and/or automatically. According to the invention it is preferable to control the phase shifter by a temperature-controlled regulator. The latter may be provided, according to another feature of the invention, with a device which determines the control limit. Such a system renders it possible to protect in a simple manner the furnace charge against overheating. A regulating system, as just described, is used in the embodiment shown in Fig. l. The thermo-responsive regulating means comprise a transmission mechanism 6| which includes a cam gear 62, further a motor 63 for actuating the gear 62, and a thermocouple 64 for controlling the motor. The thermocouple 64 is arranged at the furnace so that the phase position of source i8 and therewith the voltage or energy of the high-frequency current fed through the translating system and the transformer 4 into the furnace coil 5 is varied in response to variations of the furnace temperature. The cam gear 62 is preferably so designed that upon the attainment of a predetermined furnace temperature the voltage supplied to the furnace is automatically regulated downwards to such an extent that the losses of the furnace are compensated for. The furnace temperature then remains constant. The downward regulation of the voltage is effected practically without losses.

The invention, in one of its further aspects, also provides means for rendering the just-mentioned temperature limit adjustable so as to suit various control requirements. A control system of such type is particularly advantageous when using a static phase shifter, for instance, an arrangement of saturable magnetic circuits which, besides their main winding, have a temperature-responsive control winding. The control winding may be supplied with direct current. By means of a thermo-electric couple it is further possible to energize the control winding by a temperature-responsive exciting current superposed on a current, for instance direct current, whose amplitude is adjustable at will. A saturable magnetic phase-shifter of such design allows adjusting the control characteristic of the translating system to any desired control limit. This will be apparent from the following description of the embodiment of Fig. 2 showing a regulatable translating system of the last-mentioned type.

The embodiment represented by Fig. 2 is similar to that of Fig. l as far as the furnace, the

.main discharge vessel 3, the main supply transformer 2, the controlling high-frequency source I2 and several appertaining circuit elements are concerned. .For simplicity, these identical elements are omitted in Fig. 2. The transformer windings I4, the vessel l5 and the controllable rectifier units housed therein, the transformers I! and the grid voltage source l6 and resistances l9, shown in Fig. 2, have the same arrangement and function as the corresponding elements of Fig. 1. However, the phase-controllable lowfrequency source H! of Fig. 1, and the appertaining auxiliary elements are replaced in Fig. 2 by the control means presently to be described.

Each phase of the low-frequency control voltage is supplied from the terminals R, S, T, respectively, through a phase shifter 20 to the corresponding transformer |1. In this case a bridge network consisting of induction coils 2| and resistors 22 is chosen as a phase shifter. The diagonal circuit of the bridge network contains the primary winding l8 of the transformer H. The coils 2| are arranged on a core of highly permeable material and are each provided with a control winding 2|. All control windings 2| are sezies-connected to a composite direct-current source which consists of a differential circuit arrangement and comprises two voltage sources 25 and 26 connected in opposition to each other through resistors 23 and 24. The voltage source 25 may be one of the known automatic control arrangements, for instance a thermo-electric couple, by means of which a change in the temperature or radiation of heat brings about a change in the electric current or voltage. 26 is a resistor with sliding contact energized by the direct-voltage battery 21. Furthermore, an amplifier 28 and a rectifier valve 29, preferably a dry rectifier, is provided.

For explaining the operation of the system it is assumed that the sliding contact 26 is adjusted so that the voltage-drops across the resistors 23 and 24 are the same at a desired furnace temperature of 800 degrees centigrade. When putting the furnace into operation, a current, whose intensity depends upon the difference between the furnace temperature of 800 degrees centigrade and the actual furnace temperature, flows through the series-connected coils 2| of the saturable reactors. These reactors are so dimensioned that the inductance of the coils 2| and therefore the phase advancement of the low frequency control voltage increase rapidly to a value which corresponds to the full control of the main discharge device; i. e. the furnace is now supplied with a current of high intensity. If the furnace temperature approaches 800 degrees centigrade, the current flowing through the control windings 2|' of the coils 2| decreases to the same extent due to the control effected by the thermocouple 64. As a result, the inductance of the coils 2|, i. e. the phase leading of the lowfrequency control voltage and therefore the control of the main discharge device, approaches a state of equilibrium at which only the losses of the furnaces are compensated for. A reversal of the mentioned differential current supplied by the voltage sources 21 and 25 is prevented by the rectifier valve 29.

According to a further feature 'of the invention, the phase shifter inserted in the supply conductor of the low-frequency control voltage is coupled to an automatic device for changing the phase position of the low-frequency control voltage according to a desired or predetermined characteristic. This allows a temperature control of the furnace charge according to a predetermined scheme. 1

In this case it is again preferable to use saturable magnetic circuits as a static phase shifter. The saturable magnetic circuits are provided with an additional control winding whose excita-.

tion may be varied in any'suitable manner. For instance, the control winding may be excited by direct current which is controlled by a resistor having a slide contact operated by the curvilinear surface of a cam, as will be explained in detail hereinafter.

Another form of the invention consists in connecting the phase shifter of the low-frequency control voltage to a regulator which is controlled by the furnace current and provided with a device for adjusting the desired temperature value. The invention thus provides the possibility of selecting any desired datum temperature and of maintaining the furnace temperature constant at this datum value by regulating the furnace current practically without losses. Also in this case the invention uses preferably a static phase shifter consisting of an arrangement of saturable magnetic circuits similar to those mentioned above. The magnetic circuits are provided with an additional control winding whose excitation, particularly a direct-current excitation, is

controlled in accordance with the furnace current.

The means according to the invention for selecting the datum value of the furnace current or temperature to be kept constant, comprise two control windings which are associated with the magnetic circuits in addition to the main reactance windings of these saturable circuits. One of the additional control windings is so designed and energized that it tends to effect a full control of the main discharge device, whereas the other control winding acts oppositely thereto. The counteracting winding is energized by a resultant control current having a component responsive to the furnace current, and a second component which may be arbitrarily chosen. The latter determines the desired value of the furnace current and may be taken from a regulatable direct-current source. The component responsive to the furnace current may be obtained with the aid of a current transformer which is inserted at the primary side in the circuit of the furnace coil.

The embodiment of the invention illustrated in Fig. 3 serves to elucidate the last-mentioned modifications. In Fig. 3 the discharge vessels 3 and i5 shown in Figs. 1 and 2, as well as the intermediate circuit elements, the main supply transformer and the furnace apparent from Fig. 1, are omitted for the sake of clearness.

The transformer has itsprimary 30 inserted in the circuit of the furnace coil, and its secondary connected to a resistor 32 through a rectifier 3|. A second resistor 33 is connected to the first-mentioned resistor directly as well as through a third resistor 34. 'Besides, the resistor 33 is connected to the control contact 65 of a resistor 35, supplied with direct-current from source 36. As mentioned before, the adjustment of the datum value may be effected in accordance with a predetermined characteristic, for instance, by employing a cam mechanism for actuati'ng the slide contact 65. Such a mechanism the terminals l2 in Fig. 1.)

is shown in Fig. 3; it comprises a cam gear 88 connected with slide contact 35 by a tappet member 69. A motor I0 serves to rotate the cam at uniform speed. The cam curve corresponds to the predetermined characteristic of the control operation and is selected to suit the particular metallurgical or other operation to be carried out by the furnace.

The position of the control contact determines the datum value of the furnace current to be regulated. The resistor 34 is inserted in the negatively biased circuit of an amplifier valve 3'! through which the series-connected control windings 2| of the saturable inductance coils 2! are energized by the direct-voltage'source 33. A second control winding 20 is magnetically associated with the maincoil 2| and the first control winding 21' of each reactor unit. The secand control windings 20' are series connected to another direct-voltage source 39. The magnetization of the reactor units effected by the windings 20 is so rated, by properly adjusting the energizing current from source 33, that it imparts to the coils 2i an inductance value and therefore to the low-frequency control voltage component a position of phase which correspond to the full control of the main discharge devices. The circuit of the voltage source 39 contains a device for determining the starting periods. This device comprises a resistor 40 and a condenser 4 its operation will be described in a later paragraph. As in the embodiment shown in Fig. 2 the phase shifter 20 consists of a bridge network formed of the inductances 2i and ohmic resistors 22. Also in this case the low-frequency control voltages are supplied to the discharge devices by means of transformers l1 whose primaries iii are inserted in the diagonal branch of the bridge network 20.

42 designates an overcurrent control relay 42. The main actuating coil 43 of this relay is connected to the rectifier 3|. The relay contains a self-holding device consisting of a coil 48, a time relay 50 and the contact switches 45 and 43. The'switches 45 are actuated by the armature 41 of coils 43 and 43 together with the switches designated by 44 and 46. Contact 49, however, is opened and closed by the time relay 50. The time relay 50 is excited when the two switches 45 engage their respective left-hand contacts 45'. 5| designates the source of the highfrequency control voltage whose frequency determines that of the furnace current. (The terminals I! are equivalent to, or connected with, The control switch 46 serves to set the voltage source 5| in and out of operation. When the switches 45 come into engagement with their left-hand contact 45 the control voltages of the main discharge devices decrease below the ignition value.

The operation of the system will now be described, at first without considering the overload control relay 42 and the device 40, 4|.

If upon the increase of the furnace coil current the voltage across the resistor 32 exceeds the value of the voltage drop across the resistor 33, the voltage drop across 34 reverses. As a result, the resistor 34 supplies the grid of the amplifier valve 31 no longer with a negative but with a positive voltage so that a current flows through the control windings 21 in a direction opposite to the flow of the current supplied from the voltage source 39 through the second control windings 20'. The inductance of the coils 2| is reduced, and therefore the phase of the voltages supplied to the transformers I'I changes in a manner so that the main discharge devices are not controlled to the full extent. Consequently, the furnace coil current decreases to such an extent as to obtain the same voltage drops across the resistances 32 and 34. The current is adjusted to a value which is determined by the position of the control contact 65 on the resistor 35.

Reverting now to the overload relay 42, its operation and purpose will be understood from the following. As stated before, the actuating coil 43 of the relay 42 is connected to the rectifier 3| and hence through transformer 30 with the furnace coil. The current in relay coil 43 thus is dependent upon the furnace current. If the furnace current exceeds a certain value, the coil 43 is sufficiently energized to attract its armature 41 which brings switches 44, 45 and 46 in engagement with their left-hand contacts. The two switches 44 interrupt the energization of the control windings 2| and 20'. As a result, the phase-regulating network 20, properly dimensioned for this effect, reduces the phase angle of the low-frequency control voltage to such an extent that the main discharge devices are blocked and remain non-conducting. Thus, the furnace coil is cut out instantaneously. At the same time, the time relay 50 is energized so that the switch 59 and therefore the self-holding circuit of the relay 42 are closed. The coil 48 firmly holds the armature 41 in the position assumed, until the time relay opens the switch 49 after a period adjustable at the time relay. The switches 44 to 46 then come into engagement with their right-hand contact. The control windings 2| and 20 are again energized. The exciting current supplied by the source 39 and corresponding to the full control of the discharge devices attains its end value within a regulatable starting period determined by the resistor 40 and the capacitor 4|.

A protective overload-responsive device of the character exemplified by relay 42, which may also contain controllable discharge tubes instead of the electromechanical switches shown, effects an instantaneous disconnection and a subsequent timely controlled putting into operation of the translating system upon the occurrence of overloads such as caused by flashovers at the furnace coil. This distinguishes the system favorably from the feeding systems hitherto employed, which, in practice, do not afford an overload protection of instantaneous operation,

Another inventive feature embodied in the above-described translating system is the combination of the phase shifter with a starting device having an adjustable starting period. If an overload of the furnace coil causes a disconnection of the system, or if the voltage supplied to the furnace is regulated to the zero value by the control grids; the operating voltage is automatically reestablished after the elapse of an interval determined by a time relay and within an adjustable starting period or rate of change.

Translating systems, according to the invention, for supplying induction furnaces with highfrequency current from a low-frequency energy source obtain an improved economy together with a greater accuracy of control than the conor rate of change, than are often to be dealt with in metallurgical processes. However, the invention is not limited to such induction furnaces, but is also of advantage in connection with other purposes requiring a controllable supply to an electric device of current having a higher frequency than that of the current source proper.

What is claimed is:

1. In an electric translating system for transtrollable means for bridging said resistance means at the low frequency of said supply circuit, said bridging means including a set of controllable rectiflers having a cathode circuit, each of the rectifiers of said set having two anodes for fullwave operation, transformers each having one winding connected with said resistance means to individually bridge one of said resistance means and the other winding connected between said two anodes of an individual rectifier of said set, each of said latter transformer windings having a tap connected with said cathode circuit, and phase-adjusting control means associated with said rectifiers and comprising a low-frequency voltage source for controlling said rectifiers at the frequency of said load circuit.

2. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of a main discharge device of rectifierconverter construction having two anodes and two respective control electrodes for each phase of said supply circuit, a, transformer arrangement connecting said anodes with said load circuit and said supply circuit for translating the low-frequency supply current into the high-frequency load current, and control means associated with said main-discharge device for determining the-frequency and energy of said load current, said control means including a high-frequency voltage source, a first transformer for transmitting a control voltage from said source to both said control electrodes of each phase, a resistor series-connected with said highfrequency source and said first transformer for controlling the amplitude of said control voltage and a second transformer having one winding connected in parallel to said resistor, the other winding of the latter transformer being tapped, an auxiliary discharge device having for each phase two anodes and control electrodes for fullwave rectification, a common cathode and a common vessel enclosing said anodes, electrodes and cathode, said two anodes of each phase being connected with the ends of said tapped transformer winding and said taps being connected with said common cathode, in combination with phase-adjustable control means connected with said control electrodes of said auxiliary discharge device and including an auxiliary low-frequency voltage source for controlling said auxiliary discharge device at the frequency of said supply circuit.

3. With a translating system as set'forth in claim 2, in combination, an adjustable resistance series-connected between said control electrodes of said main discharge device and said first transformer, and the aforesaid resistor series connected with said first transformer and said high-frequency voltage source being also of ad- Justable type.

4. With a translating system as set forth in claim 2, in combination, a circuit containing a reactor connected between said transformer ar rangement and the cathode of said main discharge device.

5. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source.

6. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of a plurality of pairs of controllable discharge devices, a. multiphase transformer having primaries connected with said supply circuit and secondaries connected each with the two discharge devices of one of said pairs respectively, transformer means interconnected between said secondaries and said discharge devices respectively and coupled with said high-frequency load circuit, condenser means interconnected between said two discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source.

7. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said. discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between the two discharge devices of each of said pairs respectively, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, phase-adjustable voltage supply means, said lattermeans being connected in said control circuit having the low frequency of said supply circuit of each pair -for controlling the amplitude of said high-frequency voltage.

8. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between each of said pairs of discharge devices, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, resistance means for controlling the amplitude of said high-frequency voltage, controllable means for bridging said resistance means periodically at the low frequency of said supply circuit, and phase-adjustable low-frequency control means associated with said bridging means for controlling the bridging moments.

9. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser meansinterconnected between said pairs of discharge devices, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, resistance means for controlling the amplitude of said high-frequency voltage, and controllable means for bridging said resistance means at the low frequency of said supply circuit, said bridging means including a set of controllable rectifiers having one cathode circuit, each of the rectifiers of said set having two anodes for full-wave operation, transformers each having one winding connected with said resistance means to individually bridge said resistance means respectively and another winding connected between said two anodes of the individual rectifiers respectively of said set, each of said latter transformer windings having a tap connected with said cathode circuit, and phase-adjustable control means associated with said rectifiers and comprising a low-frequency voltage source for controlling said rectifiers at the frequency of said load circuit.

10. In an electric translating system for transmitting energy between a low-frequency multiphase supply circuit and a high-frequency load circuit, the combination of a main discharge apparatus having a pair of anodes and a corresponding pair of control electrodes for each phase of said supply circuit, condenser means interconnected between said two anodes of each pair, a transformer arrangement connecting said anodes with said load circuit and said supply circuit for translating the low-frequency supply current into the high-frequency load current, and control means associated with said main discharge apparatus for determining the frequency and energy of said load current, said control means including a high-frequency voltage source. a first transformer for transmitting a control voltage from said source to both said control electrodes of each phase, a resistor series-connected with said high-frequency source and said first transformer for controlling the amplitude of said control voltage, and a second transformer having two windings, one of said windings being connected in parallel to said resistor, said other winding being tapped, an auxiliary discharge device having for each phase two anodes and two control electrodes for full-wave rectification, a common cathode, and a common vessel enclosing said latter anodes, electrodes and cathode, said latter two anodes of each phase being connected with the ends of said tapped transformer winding and said taps being connected with said common cathode, in combination with phase-adjustable control means connected with said control electrodes of said auxiliary discharge device and including an auxiliary low-frequency voltage source for controlling said auxiliary discharge device at the frequency of said supply circuit,

11. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between each of said pairs of discharge devices, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a highfrequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, resistance means for controlling the amplitude of said high-frequency voltage, controllable means for bridging said resistance means periodically at the low frequency of said supply circuit, and phase adjustable lowfrequency control means associated with said bridging means for controlling the bridging moments, and temperature-responsive regulating means operatively connected with said phase-adjustable control means for automatically regulating the transmitted energy.

12. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between each of said pairs of discharge devices, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, resistance means for controlling the amplitude of said high-frequency voltage, controllable means for bridging said resistance means periodically at the low frequency of said supply circuit, and phase adjustable low-frequency control means associated with said bridging means for controlling the bridging moments, a temperature-responsive regulating means operatively connected with said phase-adjustable low-frequency control means, and adjusting means associated with said regulating means for varying the temperature control limit of said regulating means.

13. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable control means comprising a phase shifter and an actuating device operatively connected with said phase shifter for automatically adjusting said phase shifter in accordance with a predetermined control characteristic.

14. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable control means comprising a static phase shifter having saturable reactors of controllable inductance, control windings magnetically associated with said reactors, and energizing circuit means connected with said control windings for varying said inductance.

15. In an electrictranslating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable'discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit,- condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable control means comprising a static phase shifter having saturable reactors of controllable inductance arranged in said control circuit, control windings magnetically associated with said reactors, and temperature-responsive energizing means connected with said control windings for varying said inductance;

16. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in par ticular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable control means comprising a static phase shifter having a saturable reactor of variable inductance arranged in said control circuit, and two control windings magneticallv associated with said reactor so as to counteract each other, regulating means connected with one of said control windings for automatically varying the energization of said winding, and a voltage source adjustable at will connected with said other control winding.

1'7. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a

control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprisinga high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit-and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable control means comprising a static phase shifter having saturable reactors of controllable inductance arranged in said control circuit, control windings magnetically associated with said reactors, an additional voltage source for energizing said control winding, a slide contactor connected with said control windings and said additional voltage source for controlling said energlzation, and a cam mechanism for actuating said slide contact in accordance with a given control characteristic.

18. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C, rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between each of said pairs of discharge devices, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, resistance means for controlling the amplitude of said high-frequency voltage, controllable means for bridging said resistance means periodically at the low frequency of said supply circuit, and phase-adjustable low-frequency control means associated with said bridgmg means for controlling the bridging moments, said phase-adjustable low-frequency control means comprising a phase shifter arranged in said control circuit, and means responsive to the current in said load circuit for controlling said phase shifter.

19. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency contro1 voltage source, said phase-adjustable control means comprising a phase-shifter arranged in said control circuit, means responsive to the current in said load circuit for controlling said phase shifter so as to maintain a datum value, and means for adjusting said datum value.

20. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable control means comprising a static phase shifter having saturable reactors of controllable inductance arranged in said control circuit, control windings magnetically associated with said reactors respectively, and circuit means connecting said control winding with said load circuit for energizing said control winding in accordance with the load circuit current.

21. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase adjustable control means comprising a static phase shifter having saturable reactors of controllable inductance arranged in said control circuit, control windings magneticfurnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. 'C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D.- C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control-circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable control means comprising a static phase shifter having saturable reactors of variable inductance arranged in said control circuit, and two control windings associated with each of said reactors so as to counteract each other, one of said control windings being connected with said load circuit to be energized in ally associated with said reactors respectively,

response to variations of the load current, and adjustable circuit means connected with said other control winding for energizing said latter winding at will.

23. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said disoharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuitcomprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable control means being rated for a complete blocking of said discharge devices when adjusted to the minimum control value.

24. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, and phase-adjustable control means associated with said low-frequency control voltage source, said phase-adjustable low-frequency control means containing a static phase shifter arranged in said control circuit and consisting of a bridge network having pairs of opposite bridge branches, an ohmicresistor and a saturable reactor arranged in said branches respectively of each pair, an auxiliary voltage source connected with the input circuit of said bridge network and having the frequency of said load circuit, the output diagonal of said bridge network being connected with said resistance means, control windings magnetically associated with said saturable reactors, and variable energizing means connected with said control windings.

25. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condensermeans interconnected between said discharge devices of each of said pairs, a control circuit associated with said discharge devices for controlling the transmitted ener y, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, a control voltage source connected with said control circuit and having the low frequency of said supply circuit for periodically suppressing said ignition impulses in said discharge devices, phase-shifting means associated with said low-frequency control voltage source, and an overload-responsive control device coupled with said load circuit and operatively connected with said phase-shifting means.

26. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between each of said pairs of discharge devices, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, resistance means for controlling the amplitude of said high-frequency voltage, controllable means for bridging said resistance means periodically'at the low frequency of said supply circuit, and phase-adjustable lowfrequency control means associated with said bridging means for controlling the bridging moments, an overload responsive control device coupled with said load circuit and connected with said phase-adjustable control means so as to adjust said phase-adjustable control means to the blocking of said discharge devices, said control device having self-holding means, and a time relay for releasing said self-holding means in order to automatically return said phase-ad- Justable control means into non-blocking condition.

27. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C. rectifier circuit connected with said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between each of said pairs of discharge devices, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a highfrequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, resistance means for controlling the amplitude of said high-frequency voltage, controllable means for bridging said resistance means periodically at the low-frequency of said supply circuit, and phase-adjustable lowfrequency control means associated with said bridging means for controlling the bridging moments, and a starting device associated with said control circuit for adjusting the starting time of the system.

28. In an electric translating system for transmitting energy between a low-frequency supply circuit and a high-frequency load circuit, in particular for operating high-frequency induction furnaces, the combination of groups of pairs of controllable gas discharge devices, a reactive D. C. rectifier circuit connectedwith said discharge devices, transformer means connected with said discharge devices and said D. C. circuit and coupled with said supply circuit and said load circuit, condenser means interconnected between each of said pairs of discharge devices, a control circuit associated with said discharge devices for controlling the transmitted energy, said control circuit comprising a high-frequency voltage source for producing in said discharge devices ignition impulses of the frequency of said load circuit, resistance means for controlling the amplitude of said high-frequency voltage, controllable means for bridging said resistance means periodically at the low frequency of said supply circuit, and phase-adjustable low-frequency control means associated with said bridging means for controlling the bridging moments,

said phase-adjustable control means comprising a static phase shifter having saturable reactors of variable inductance arranged in said control circuit, and two control windings magnetically associated with said reactor so as to counteract each other, regulating means connected with the first of said control windings for automatically varying the energization of said winding and a voltage source adjustable at will connected with the second of said control windings, an overload relay connected with said load circuit and having relay contacts connected in the circuit of said regulating means and said first control winding, and means for determining the starting time comprising a resistor and a capacitor arrangement inserted in the circuit of said second control winding.

KLAUS FREUDENHAMMER. 

